1. Presented By: Sanku Konai
Estimation of Lateral Earth Pressure on Cantilever Sheet Pile using Flat Dilatometer Test (DMT) Data: Numerical Study
Kousik Deb & Sanku Konai
The 3rd International Conference on the Flat Dilatometer, 14th -16th June 2015, Rome, Italy
Presented By: Sanku Konai
ABSTRACT
Effect of K0 on earth pressure under different soil consistency
In the present paper, a numerical study has been conducted to estimate the lateral earth pressure acting on cantilever sheet pile using Flat Dilatometer Test (DMT) Data. The numerical analysis is done using computer program FLAC (Fast Lagrangian Analysis of Continua). The unit weight of soil, undrained cohesion, the coefficient of lateral earth pressure at rest, the stiffness of the soil layers are calculated by using the DMT data. The DMT data presented by Anderson et al. (2006) is used in the present study. The results of the present numerical analysis are compared with the measured filed data where Flat Dilatometer Test has been conducted to estimate the soil properties. Based on the numerical results, simplified earth pressure distribution is proposed for cantilever sheet pile.
Fig. 10. Effect of K0 on earth pressure (soil with stiff consistency, cu = 100 kPa)
Fig. 11. Effect of K0 on net earth pressure (soil with stiff consistency, cu = 100 kPa)
Fig. 12. Effect of K0 on earth pressure (soil with medium consistency, cu = 47.5 kPa)
Fig. 14. Effect of K0 on earth pressure (soil with soft consistency, cu = 25 kPa)
Fig. 15. Effect of K0 on net earth pressure (soil with soft consistency, cu = 25 kPa)
Fig. 13. Effect of K0 on net earth pressure (soil with medium consistency, cu = 47.5 kPa)
OBJECTIVES
Numerical study has been conducted to estimate the lateral active and passive earth pressure acting on cantilever sheet pile using Flat Dilatometer Test data. The earth pressure below the excavation depth is also estimated. The present study is based on Anderson et al.'s (2006): (a) DMT results (b) cantilever behavior observed in the field and both Anderson et al. (2006) and present study have used DMT results to predict cantilever behavior. Based on the numerical results under various excavation depths, thickness of the wall and soil properties, earth pressure distribution is proposed for cantilever sheet pile.
Sheet piles De H
Effect of deflection of sheet pile on earth pressure
Fig.1 Cross sectional view of the chosen problem of cantilever sheet pile
NUMERICAL MODELING
The vertical boundary is set at 30m from the wall. The horizontal boundary of the analytical mesh is taken at 20m below ground level.
Both horizontal and vertical movements are restrained along the bottom boundary and the vertical boundaries are restrained only against horizontal movements
The mesh size is selected as 0.1m x 0.2m.
Mohr-Coulomb” model has been used to model the soil
The friction angle of the soil is taken as zero. The average value of KD and ED are considered as 6 and 122 bar, respectively. The average cu value is taken as 47.5 kPa. The average E value of the soil is calculated as 19.5 MPa. The unit weight of the soil () is considered as 18 kN/m3. The value of K0 is limited to 1.
Fig. 16. Effect of deflection of sheet piles on earth pressure (cu = 25 kPa, K0 =1) [2m excavation depth has smaller sheet pile deformation as compared to the 6.1 m excavation depth]
PROPOSED Simplified EARTH PRESSURE diagram
Simplified proposed earth pressure diagram for different sheet pile deformation
Fig.19. Simplified proposed net earth pressure distribution (for higher sheet pile deformation)
Fig. 18. Simplified proposed active and passive earth pressure distribution (for higher sheet pile deformation)
Fig.17. Simplified proposed net earth pressure distribution (for lower sheet pile deformation)
Fig. 2 DMT profiles of the soil (Anderson et al., 2006)
RESULTS
Validation
Validation of numerical results with field data given by Anderson et al. (2006)
Fig. 3. Comparison of the lateral displacement profile obtained from present study and from field data
Fig. 4. Comparison of the net earth pressure profile obtained from present study and from field data
CONCLUSIONS
The results of the present study show mainly two types of definite pressure distribution one for stiff soil (or sheet pile with lower amount of deformation) and other for soft soil (or sheet pile with higher amount of deformation).
Sheet pile thickness is not affecting the earth pressure distribution significantly.
Similar trend is observed between the earth pressures distributions obtained with different excavation depths.
Poisson’s ratio of soil doesn’t have significant effect on earth pressure distribution.
K0 plays an important role on the earth pressure distribution of cantilever sheet pile especially above the depth of the excavation for sheet pile in medium and stiff nature of soil.
Deformation of the sheet pile is also a very important factor to choose proper earth pressure distribution along with the type of soil.
Based on the observed pressure distribution diagrams, simplified earth pressure distributions are proposed for soil with soft and stiff consistency or sheet piles with higher and lower amount of deformation. The correlations or values for the pressure distribution are also suggested based on the soil properties obtained from DMT data.
Parametric studies
Effect of sheet pile thickness, sheet pile length, excavation depth, Poisson's ratio and soil consistency on earth pressure
Fig. 5. Effect of sheet pile thickness on earth pressure
Fig. 6. Effect of sheet pile length on earth pressure
 Fig. 7. Effect of excavation depth on earth pressure
Fig. 8. Effect of  on earth pressure
Fig. 9. Effect of soil consistency on earth pressure
REFERENCES
Anderson, J. B., Ogunro, V.O., Detwiler, J.M. and Starnes, J.R. (2006). “DMT Testing for the Estimation of Lateral Earth Pressure in Piedmont Residual Soils.” Proceedings from the Second International Conference on the Flat Dilatometer, Washington, D.C., April 2-5,
Bilgin, O. (2012). “Lateral Earth Pressure Coefficients for Anchored Sheet Pile Walls.” International Journal of Geomechanics, 12(5),
Itasca (2005). User’s guide for FLAC version 5.0.
Ruffing, D. G., Evans, J.C and Malusis, M.A. (2011). “Evaluations of lateral earth pressure in a soil-bentonite slurry trench cutoff wall.” 14th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, Toronto, Ontario, Canada, 1-5.
CONTACT: Kousik Deb, Indian Institute of Technology Kharagpur, Kharagpur, India. Sanku Konai , Indian Institute of Technology Kharagpur, Kharagpur, India.